C++ Virtual Destructor with Unresolved externals

Question

I have two classes..

template <class T>
class Node
{
protected:
    Node() = default;
    virtual ~Node() = 0;
    Node(const T& data) noexcept;
    Node(const Node<T> & copy) noexcept;
    Node(Node<T> && copy) noexcept;
    Node<T> & operator=(const Node<T> & rhs) noexcept;
    Node<T> & operator=(Node<T> && rhs) noexcept;
public:
    T & GetData() noexcept;
    T GetData() const noexcept;
    void SetData(const T & data) noexcept;
private:
    T data_;
};


template<class T>
class ListNode : public Node<T>
{
public:
    ListNode() = default;
    ListNode(const T& data, ListNode<T> * next = nullptr, ListNode<T> * previous = nullptr) noexcept;
    ListNode(const ListNode<T> & copy) noexcept;
    ListNode(ListNode<T> && copy) noexcept;
    ~ListNode() override = default;
    ListNode<T> & operator=(const ListNode<T> & rhs) noexcept;
    ListNode<T> & operator=(ListNode<T> && rhs) noexcept;
    ListNode<T> * GetNext() noexcept;
    ListNode<T> * GetPrevious() noexcept;
    void SetNext(ListNode<T> * const next) noexcept;
    void SetPrevious(ListNode<T> * const previous) noexcept;
private:
    ListNode<T> * next_;
    ListNode<T> * previous_;
};

I get an "1 unresolved externals" error. In my previous experience this would usually mean something is wrong with virtual, override, or something like that. I've messed around with this code but can't make the error go away. Any advice?

The particular answer on the master question is https://stackoverflow.com/a/12574407/103167 — Ben Voigt, Jul 12 '18 at 23:02

alter_igel · Accepted Answer · 2018-07-12T22:16:32.610

4

Derived destructors always implicitly invoke the base destructor at the end of their execution. You have code that is trying to invoke an abstract function. You need to give ~Node() a definition with an empty function body:

virtual ~Node() {};

edited Jul 12 '18 at 22:16

answered Jul 12 '18 at 22:13

alter_igel

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"Deleted" means something very specific since C++11. That destructor is not a deleted function. – Ben Voigt Jul 12 '18 at 22:15
2

Note that `~Node()` is not *deleted*, it is *pure abstract*. If it were *deleted*, it would have to had been declared like `~Node() = delete;` instead. – Remy Lebeau Jul 12 '18 at 22:15
Worked. Thanks! – Jared Jul 12 '18 at 22:18

C++ Virtual Destructor with Unresolved externals

1 Answers1